In order to evaluate the effect of irrigation intervals on the vegetative growth and grain yield of grass pea (Lathyrus sativus L.)and hairy vetch (Vicia villosa Roth.), a field split plot experiment was conducted based on the randomized complete blocks design with four replications in research farm of Vali–e–Asr University of Rafsanjan during April to July, 2013. Main plots were irrigation levels including 40, 60, 80 and 100 mm evaporation from evaporation pan class A and sub plots were crop species in two levels as grass pea and hairy vetch. Result showed that 66 days after sowing (two weeks before flowering), relative water content (RWC) of grass pea and hairy vetch leaves significantly reduced by increasing irrigation amount more than 40 mm, however there were no significant differences between 60, 80 and 100 mm. Also, plant leaf area and biomass of grass pea and vetch were reduced by increasing irrigation level (77 and 73 percent, respectively). Both crops had similar biomass (1.1 and 1.2 g. plant ^-1 for control and 0.5 and 0.6 for 100 mm irrigation treatments for grass pea and vetch, respectively), while the grass pea had higher leaf area than hairy vetch (4 to 9 folded). Finally, yield and yield components of both crops decreased by irrigation interval, although grass pea had always higher yield components, as grain yield, 1000 grains weight, seed number and pod number per plant at 100 mm irrigation treatment were 4.8, 2.4, 3.7 and 3.2 fold higher than vetch. Results suggest that both crops well tolerated increasing irrigation interval and they were suitable for forage production if harvested at the flowering stage. However, grass pea was better for grain production and had higher drought tolerance.